The covalent attachment of saccharide residues to glycoproteins proceeds in a stepwise manner, certain residues being attached in different cellular compartments. Preliminary data suggest that the attachment of saccharides to the glycoprotein components of the cellular membranes may proceed similarly. These residues appear to be localized to only one surface in plasma membranes (the outer surface) and rough membranes ( the cisternal surface). The precursor membrane hypothesis (Fig.1) suggests that membrane components are assembled at the RER, then transmitted and converted into smooth membranes and Golgi elements, where they are formed into vesicles which then fuse with already existing plasma membrane. The investigations proposed in this application will determine the distribution of saccharides in the intracellular and plasma membranes and their localization to one or both surfaces of the membrane. The proposed investigation is designed to test the validity of the precursor membrane hypothesis and the results may be expected to bring out any important differences which exist in the biogenesis of normal and neoplastic cellular membranes.